Simplify the following expression: $z = \dfrac{5y}{7} + \dfrac{y}{3}$
Explanation: In order to add expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $7$ and $3$ $\lcm(7, 3) = 21$ $ z = \dfrac{3}{3} \cdot \dfrac{5y}{7} + \dfrac{7}{7} \cdot \dfrac{y}{3} $ $z = \dfrac{15y}{21} + \dfrac{7y}{21}$ $z = \dfrac{15y +7y}{21}$ $z = \dfrac{22y}{21}$